Fluvial sediments transported by rivers, such as dissolved mineral content and floating or suspended mineral content and rubble or sediment are of ecological significance for rivers. In particular, the sediment is transported out of the river in salts or rubble. Furthermore, there is suspended sediment in the river, which floats substantially free in the water columns. In undeveloped rivers, sedimentation processes, i.e. the depositing of the sediment transported in the fluvial, and erosion processes, i.e. the removal of sediments, is normally at an equilibrium. If a body of water is dammed, the flow cross section of the river changes over broad ranges. As a result of these cross section changes, the current speed slows down, wherein the sediment is deposited and is no longer transported. Consequently, increasing amounts of sediment are deposited in dammed bodies of water. The same applies for reservoirs, e.g. from hydropower plants, where the water remains relatively calm between individual operating procedures, i.e. pumping and turbine operations. On one hand, the increasing sediment on the ground in dammed bodies of water reduces the capacity of the dammed body of water, and on the other hand, the fluvial sediment is missing in the downstream water, i.e. the water located downstream of the dam.
The fluvial sediment is needed in rivers in order to counterbalance sedimentation processes at other locations. This affects flood protection in particular, because rivers free of sediment transport water more quickly, such that flood waves progress more quickly, and also have greater amplitudes. There is frequently stronger erosion at the bases of a dam or a retaining wall, which may compromise the stability of the dam making it unsafe. In addition to water, solids, living organisms, gases, e.g. carbon dioxide, oxygen, methane and other gases resulting from decomposition, and energy, in particular in the form of flow speeds and temperature, are transported in rivers. If the transport is prevented through blockages, or strongly compromised, there are also ecological consequences downstream of the dam. There are frequently fewer nutrients contained in water when suspended matter has deposited in dammed bodies of water. Furthermore, the retention of solid matter, such as rocks, sand and gravel, can increase the flow speed in the downstream water. The energy that would otherwise be applied for transporting fluvial sediment is then consumed entirely by the flow speed of the water. The flow speed increased in this manner has a greater erosion effect on the riverbed, resulting in further increase in the flow speed, and channels being cut into the riverbed.
A further disadvantage with dammed bodies of water is that already at a sediment depth of approximately 2 cm of the deposited sediments, decomposition processes of organic matter can only take place anaerobically. This leads to an increased discharge of methane. Taking into consideration the large number of barrages present in individual, navigable dammed bodies of water, including those used for generating energy from hydropower, the output of methane from dammed bodies of water is immense.
Methods are known from the prior art, which provide a transportation of sediment deposits in dammed bodies of water. Thus, EP 2 134 902 B1 describes a method for transporting sediments in hydropower plants, wherein the sediment deposit is collected in the sediment region of the reservoir, and the accumulated sediment deposits are transported to the erosion region of the reservoir in the vicinity of the discharge organ.
The object of the present specification is to improve the known prior art.